Lesson plan

# 9. Add and subtract to find differences in length (FP)

teaches Common Core State Standards CCSS.Math.Content.2.MD.A.4 http://corestandards.org/Math/Content/2/MD/A/4
teaches Common Core State Standards CCSS.Math.Practice.MP3 http://corestandards.org/Math/Practice/MP3

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Lesson objective: Add and subtract to compare measured or estimated lengths of objects.

This lesson helps to build procedural skills with finding length differences through addition and subtraction. An inch ruler is used here because it supports the connection between length and addition/subtraction. This work develops students' understanding that both operations can be used to find length differences.

Students engage in Mathematical Practice 3 (Construct viable arguments and critique the reasoning of others) as they present and defend their equations.

Key vocabulary:

• difference

Special materials needed:

• classroom objects (see Game Directions in the Additional Materials tab for specifics)
• folders
• inch rulers